I've used coarse grade media of Tropical Eden, ARM, and Two Little Fish. They all look like tiny coral branches. I use whichever the cheapest (often Tropical Eden)/on sale at the time. I heard that they were coral branches rolled in a big drum to make them small and smoother. When I was short on the media (the last change), I mixed a small amount of my old coral skeletons. I have not seen any problem.